1. Field of the Invention
The present invention relates to a disk control device, a disk control method that facilitate access to disk drives in response to write commands or read commands from a host.
2. Description of the Related Art
A disk control device forms a system by being connected to a host, which is an upper interface, and to a disk drive, which is a lower interface.
If write data sent from a host is increasing so that the capacity of a cache memory becomes insufficient to store new write data sent from the host, the disk control device writes the write data of the corresponding block in the cache memory into the disk drive according to the write back method, thereby reserving a sufficient area of the cache memory for storing the write data sent from the host.
While the write data is being written back to the disk drive, many write commands from the host are stored in the processing queue of the disk control device.
In this situation, upon receiving a read command, the disk control device issues to store the read command in the processing queue for the disk drive. In this case, many write commands are already stored in the processing queue for the disk drive.
Accordingly, the read command has to wait until the write commands are written. Accordingly, the performance of the reading processing (hereinafter simply referred to as the “read performance”) is greatly influenced by write access processing.
Thus, the read performance during the write back processing is deteriorated compared to that when the write back processing is not performed.